4,366 research outputs found
New Results on Precision Studies of Heavy Vector Boson Physics
We present new results for two important heavy vector boson physics
processes: (1), virtual corrections to hard bremsstrahlung which are relevant
to precision predictions for the radiative return process in Z boson production
at and beyond LEP2 energies ; and, (2), electric charge screening effects in
single W production with finite p_T, multiple photon radiation in high energy
collider physics processes. In both cases we show that we improve the
respective precision tag significantly. Phenomenological implications are
discussed.Comment: 5 pages, 2 figures; to appear in Proc. DPF200
Invariant mass distributions in cascade decays
We derive analytical expressions for the shape of the invariant mass
distributions of massless Standard Model endproducts in cascade decays
involving massive New Physics (NP) particles, D -> Cc -> Bbc -> Aabc, where the
final NP particle A in the cascade is unobserved and where two of the particles
a, b, c may be indistinguishable. Knowledge of these expressions can improve
the determination of NP parameters at the LHC. The shape formulas are
composite, but contain nothing more complicated than logarithms of simple
expressions. We study the effects of cuts, final state radiation and detector
effects on the distributions through Monte Carlo simulations, using a
supersymmetric model as an example. We also consider how one can deal with the
width of NP particles and with combinatorics from the misidentification of
final state particles. The possible mismeasurements of NP masses through `feet'
in the distributions are discussed. Finally, we demonstrate how the effects of
different spin configurations can be included in the distributions.Comment: 39 pages, 14 figures (colour), JHEP clas
Review of Top Quark Physics
We present an overview of Top Quark Physics - from what has been learned so
far at the Tevatron, to the searches that lie ahead at present and future
colliders. We summarize the richness of the measurements and discuss their
possible impact on our understanding of the Standard Model by pointing out
their key elements and limitations. When possible, we discuss how the top quark
may provide a connection to new or unexpected physics.Comment: 84 pp. With permission from the Annual Review of Nuclear & Particle
Science. Final version of this material is scheduled to appear in the Annual
Review of Nuclear & Particle Science Vol. 53, to be published in December
2003 by Annual Reviews (http://www.annualreviews.org
Mass Determination in SUSY-like Events with Missing Energy
We describe a kinematic method which is capable of determining the overall
mass scale in SUSY-like events at a hadron collider with two missing (dark
matter) particles. We focus on the kinematic topology in which a pair of
identical particles is produced with each decaying to two leptons and an
invisible particle (schematically, followed by each
decaying via where is invisible). This topology
arises in many SUSY processes such as squark and gluino production and decay,
not to mention t\anti t di-lepton decays. In the example where the final
state leptons are all muons, our errors on the masses of the particles ,
and in the decay chain range from 4 GeV for 2000 events after cuts to 13
GeV for 400 events after cuts. Errors for mass differences are much smaller.
Our ability to determine masses comes from considering all the kinematic
information in the event, including the missing momentum, in conjunction with
the quadratic constraints that arise from the , and mass-shell
conditions. Realistic missing momentum and lepton momenta uncertainties are
included in the analysis.Comment: 41 pages, 14 figures, various clarifications and expanded discussion
included in revised version that conforms to the version to be publishe
Microsatellite analysis of albacore tuna (Thunnus alalunga): population genetic structure in the Nord-East Atlantic Ocean and Mediterranean sea
Stock heterogeneity was investigated in albacore tuna (Thunnus alalunga, Bonnaterre 1788), a commercially important species in the North Atlantic Ocean and Mediterranean Sea. Twelve polymorphic microsatellite loci were examined in 581 albacore tuna from nine locations, four in the north-east Atlantic Ocean (NEA), three in the Mediterranean Sea (MED) and two in the south-western Pacific Ocean (SWP). Maximum numbers of alleles per locus ranged from 9 to 38 (sample mean, 5.2-22.6 per locus; overall mean, 14.2 +/- 0.47 SE), and observed heterozygosities per locus ranged from 0.44 to 1.00 (overall mean: 0.79 +/- 0.19 SE). Significant deficits of heterozygotes were observed in 20% of tests. Multilocus F-ST values were observed ranging from 0.00 to Theta = 0.036 and Theta' = 0.253, with a mean of Theta = 0.013 and Theta' = 0.079. Pairwise F-ST values showed that the SWP, NEA and MED stocks were significantly distinct from one another, thus corroborating findings in previous studies based on mitochondrial DNA, nuclear DNA (other than microsatellites) and allozyme analyses. Heterogeneity was observed for the first time between samples within the Mediterranean Sea. GENELAND indicated the potential presence of three populations across the NEA and two separate populations in the Mediterranean Sea. Observed genetic structure may be related to migration patterns and timing of movements of subpopulations to the feeding grounds in either summer or autumn. We suggest that a more intensive survey be conducted throughout the entire fishing season to ratify or refute the currently accepted genetic homogeneity within the NEA albacore stock
A hybrid method for determining particle masses at the Large Hadron Collider with fully identified cascade decays
A new technique for improving the precision of measurements of SUSY particle
masses at the LHC is introduced. The technique involves kinematic fitting of
events with two fully identified decay chains. We incorporate both event ETmiss
constraints and independent constraints provided by kinematic end-points in
experiment invariant mass distributions of SUSY decay products. Incorporation
of the event specific information maximises the information used in the fit and
is shown to reduce the mass measurement uncertainites by ~30% compared to
conventional fitting of experiment end-point constraints for the SPS1a
benchmark model.Comment: 10 pages, 2 .eps figures, JHEP3 styl
Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized -Pu
The effects on the local structure due to self-irradiation damage of Ga
stabilized -Pu stored at cryogenic temperatures have been examined
using extended x-ray absorption fine structure (EXAFS) experiments. Extensive
damage, seen as a loss of local order, was evident after 72 days of storage
below 15 K. The effect was observed from both the Pu and Ga sites, although
less pronounced around Ga. Isochronal annealing was performed on this sample to
study the annealing processes that occur between cryogenic and room temperature
storage conditions, where damage is mostly reversed. Damage fractions at
various points along the annealing curve have been determined using an
amplitude-ratio method, standard EXAFS fitting, and a spherical crystallite
model, and provide information complementary to previous electrical
resistivity- and susceptibility-based isochronal annealing studies. The use of
a spherical crystallite model accounts for the changes in EXAFS spectra using
just two parameters, namely, the crystalline fraction and the particle radius.
Together, these results are discussed in terms of changes to the local
structure around Ga and Pu throughout the annealing process and highlight the
unusual role of Ga in the behavior of the lowest temperature anneals.Comment: 13 pages, 10 figure
Phenomenology of Mirror Fermions in the Littlest Higgs Model with T-Parity
Little Higgs models are an interesting alternative to explain electroweak
symmetry breaking without fine-tuning. Supplemented with a discrete symmetry
(T-parity) constraints from electroweak precision data are naturally evaded and
also a viable dark matter candidate is obtained. T-parity implies the existence
of new (mirror) fermions in addition to the heavy gauge bosons of the little
Higgs models. In this paper we consider the effects of the mirror fermions on
the phenomenology of the littlest Higgs model with T-parity at the LHC. We
study the most promising production channels and decay chains for the new
particles. We find that the mirror fermions have a large impact on the
magnitude of signal rates and on the new physics signatures. Realistic
background estimates are given.Comment: 13 p
Prospects for the Search for a Standard Model Higgs Boson in ATLAS using Vector Boson Fusion
The potential for the discovery of a Standard Model Higgs boson in the mass
range m_H < 2 m_Z in the vector boson fusion mode has been studied for the
ATLAS experiment at the LHC. The characteristic signatures of additional jets
in the forward regions of the detector and of low jet activity in the central
region allow for an efficient background rejection. Analyses for the H -> WW
and H -> tau tau decay modes have been performed using a realistic simulation
of the expected detector performance. The results obtained demonstrate the
large discovery potential in the H -> WW decay channel and the sensitivity to
Higgs boson decays into tau-pairs in the low-mass region around 120 GeV.Comment: 20 pages, 13 ps figures, uses EPJ style fil
Chern-Simons theory and three-dimensional surfaces
There are two natural Chern-Simons theories associated with the embedding of
a three-dimensional surface in Euclidean space; one is constructed using the
induced metric connection -- it involves only the intrinsic geometry, the other
is extrinsic and uses the connection associated with the gauging of normal
rotations. As such, the two theories appear to describe very different aspects
of the surface geometry. Remarkably, at a classical level, they are equivalent.
In particular, it will be shown that their stress tensors differ only by a null
contribution. Their Euler-Lagrange equations provide identical constraints on
the normal curvature. A new identity for the Cotton tensor is associated with
the triviality of the Chern-Simons theory for embedded hypersurfaces implied by
this equivalence. The corresponding null surface stress capturing this
information will be constructed explicitly.Comment: 10 pages, unnecessary details removed, typos fixed, references adde
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